Thin Film Transistors a-Si Based

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  • Topic: Thin-film transistor, Silicon, Liquid crystal display
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sedLOGIC DESIGN

THIN FILM TRANSISTORS
(AMORPHOUS MATERIAL BASED)

PALLAVI S.
1RV11IT030

CONTENTS
INTRODUCTION
EARLY DEVELOPMENTS
WHAT IS A THIN FILM TRANSISTOR?
MATERIALS USED FOR TFT CONSTRUCTION
AMORPHOUS SILICON BASED TFT
* CONSTRUCTION
* WORKING
* DEVICE MODELLING
APPLICATIONS
* TFT IN LIQUID CRYSTAL DISPLAY
FUTURE APPLICATIONS
PAPERS AND ARTICLES PUBLISHED OVER THE YEARS..
CONCLUSION
REFERENCES

INTRODUCTION

Over the past 10 years, thin film transistors (TFTs) have become critical to the growth and development of the electronic flat panel industry. Today, flat panels have become a part of everyday life. From LCD televisions to calculator displays, from mobile phones and touch sensitive displays to signboards, TFTs are omnipresent. Hence, understanding the behavior, working and construction of TFTs also becomes essential. Various reports, papers and articles that have been published over the years are crucial to this report and have been mentioned. This report covers the history and basics of thin film transistors, along with their construction of amorphous material based TFT, working and present applications. The future implications of TFTs have also been discussed.

EARLY DEVELOPMENTS
The history of thin film transistors dates back to the 1930s, when Lilienfeld invented the most primitive form of a field effect device. Though, this model was soon discarded due to incorrect claims in the patent.

Holger Heil, in his 1935 patent, presented more solid claims and correctly explained the behavior and structure of a field effect device. His claims displayed a knowledge of p type semicondutors, which were unknown till then. Later on, in 1939, Shockley developed a device based of the Schottky diode, i.e., metal-semiconductor contact. This is what we know today as the MESFET.

In the 1940s, Shockley tried a new approach focusing on simplicity of elemental semiconductors. He attempted to develop a field effect device using a germanium thin film. Though, the results to this approach were disappointing as the change in conductivity observed was far lesser than the expected value. This and an accurate explanation provided by John Bardeen led to a more in depth analysis of semiconductor properties. In 1948, Bardeen and Brattain invented the bipolar junction transistor (BJT) at Bell Laboratories, while Shockley invented the junction field effect transistor (JFET).

The 1960s was when the history of TFTs actually began to develop. P.K. Weimer at RCA Laboratories developed a device which is known today as staggered TFT structure. He worked with a CdS thin film and obtained excellent results. This was followed by F.V. Shallcross’s research which involved a CdSe thin film which produced similar results. And so, active research began in this field, using various semiconductor thin films.

TFTs truly attained mainstream status in the 1970s when research on crystalline silicon revealed that low costs as well as miniaturization could be simultaneously achieved. This brought about an exponential growth in TFT research and resulted in TFTs as we know them today.

WHAT IS A THIN FILM TRANSISTOR?

A thin-film transistor (TFT) is a field-effect transistor that is built by layering thin films on a glass substrate. This differs from the traditional diffusion into a silicon substrate more common for integrated circuits such as microprocessors. TFTs can be made using a wide variety of semiconductor materials. One common material is silicon. The characteristics of a silicon based TFT depends on the crystalline state of silicon, that is, the semiconductor layer can be either amorphous silicon, microcrystalline silicon, or it can be annealed into polysilicon. This report covers the synthesis and applications of amorphous silicon TFTs.

A thin film transistor comprises of :
* a substrate having a planar surface
* a prism shaped gate electrode positioned on said planar surface, having a...
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